The inventions described herein may be manufactured, used and licensed by or for the U.S. Government for U.S. Government purposes.
1. Field of the Invention
The present invention relates to a system for controlling the trajectory of a launched projectile. More particularly, the invention pertains to a method for correcting the displacement of a launched projectile after it is released from a launch platform using on-board control technology.
2. Description of the Related Art
The effectiveness of gun launched projectiles is directly related to the accuracy with which they can be delivered to a target. Over the years, numerous advancements have been made to gun systems that have greatly improved the accuracy with which projectiles can be delivered to the target. Among these advancements are aerodynamically stable projectiles, longer barrels, improved barrel straightness, tighter tolerances on gun-projectile interface, higher muzzle velocities, and improved sighting and fire control systems. Although these efforts have significantly improved targeting accuracy, there is constant need in the military for increased effectiveness in delivery accuracy. This need and desire for high delivery accuracy led to the development of fully guided or xe2x80x9csmartxe2x80x9d munitions. Guided munitions utilize various seekers coupled to some type of trajectory divert system (control fins, thrusters) through a closed loop control system to continuously track and maneuver toward the target.
Two categories of guided munitions systems are generally known in the art, autonomous and command guided weapons. Autonomous guided weapons generally contain control thrusters, attitude sensors, optical and/or radar based target sensors, hardware and software to accomplish target tracking, and projectile control processors for making guidance computations. Such known autonomous guided weapons include The Maverick, Stinger and Advanced Medium Range Air-To-Air Missile (AMRAAM).
Known command guided systems involve more control by an operator than automated systems. These systems generally use optical sensors or radar to image targets toward which an operator will lead the weapon, such as by tracking the weapon by a command unit that senses a beacon on the weapon and commands it via a trailing wire to fly along a line of sight. Weapons of this type, such as a Tube-launched Optically tracked, Wire guided (TOW) missile, typically carry an attitude reference gyro to define body roll position and an aerodynamic tail control system. Further, U.S. Patriot missiles are known to use attitude reference systems to cause commanded maneuvers to occur in the commanded direction. Further description of automated and command guided weapons systems can be found, for example, in U.S. Pat. No. 5,685,504.
While guided projectiles like these offer the possibility of pinpoint accuracy at extended ranges they suffer from a number of disadvantages relative to unguided projectiles. Maneuvering all the way to the target requires large divert capability which leads to large interior volume requirements. Large rounds tend to have low muzzle velocity and high drag which may lead to a need for an on board propulsion system in order to achieve acceptable terminal ballistic performance. Also, complex navigation systems employing autopilots and inertial measurement units may be needed. All of these systems tend to be costly and have survivability issues in the high acceleration gun launch environment. Guided projectiles are also difficult to develop and tend to be very costly relative to unguided ammunition. Accordingly, it is desirable to have projectiles with improved accuracy relative to unguided rounds without the complexity of a fully guided projectile. The present invention provides a solution to this need.
It has been found that eliminating or reducing projectile xe2x80x9cjumpxe2x80x9d, or the angular deviation of the flight path of a projectile relative to its intended trajectory, will greatly increase the accuracy of gun fired projectiles. Projectile jump arises from launch disturbances imparted to the projectile just prior to, during, and shortly after muzzle exit. The present invention uses on-board instrumentation and control technology for measuring projectile jump and correcting the flight path of the projectile toward its originally intended trajectory. This has been found to significantly improve delivery accuracy of a weapon, without the complexity and high cost involved with fully guided systems.
The invention provides a trajectory controlled projectile comprising:
a projectile having a longitudinal axis;
at least one pair of orthogonally positioned accelerometers within the projectile, each mounted perpendicular to the longitudinal axis of the projectile, said at least one pair of accelerometers providing projectile acceleration data to a microprocessor mounted on the projectile;
an array of thrusters mounted around an outer periphery of the projectile which are positioned to exert a thrust normal to the longitudinal axis of the projectile upon deployment by a signal from the microprocessor corresponding to the acceleration data.
The invention also provides a method for controlling the trajectory of a launched projectile comprising:
a) providing a projectile having a longitudinal axis;
at least one pair of orthogonally positioned accelerometers within the projectile, each mounted perpendicular to the longitudinal axis of the projectile, said at least one pair of accelerometers providing projectile acceleration data to a microprocessor mounted on the projectile; and
an array of thrusters mounted around an outer periphery of the projectile which are positioned to exert a thrust normal to the longitudinal axis of the projectile upon deployment by a signal from the microprocessor corresponding to the acceleration data;
b) engaging said projectile with a mounting platform and orienting said projectile in an initial target direction;
c) launching the projectile away from the platform toward a target;
d) measuring the acceleration data of the projectile with the accelerometers during and immediately after said launching away from the platform and signaling the acceleration data to the microprocessor;
e) calculating any angular deviation in the position of the projectile longitudinal axis from its pre-launch initial target direction via the microprocessor using the acceleration data; then
f) deploying one or more of the thrusters to cause a correcting thrust normal to the longitudinal axis of the projectile via a signal from the microprocessor corresponding to the acceleration data.